1. Field Of The Invention
The present invention relates to a method and apparatus for making a polymer resin impregnated, deformable molded fiber product, and a method of deforming the product. In particular, the present invention relates to a method of making a combustible, nitrocellulose shell casing from a single molding by forming the casing from a unique intermediate pulp product which can be swaged to form a reduced diameter. The invention further includes a method of forming detents in the casing by hot pressing permitting the easy attachment of a metal stub base.
2. Description Of The Background Art
Combustible shell casings have been in use as ammunition for tank guns, self-propelled Howitzers and as other ordinance items for some time. It is known to form these casings from mixtures of nitrocellulose fiber, natural cellulose fiber and synthetic fiber. This fiber mixture is accreted from a slurry on a felting die, pressed and dried in vented, mated, drying dies under vacuum to close tolerances to fit the firing chamber of a gun.
Combustible cartridge cases not only contain the main propellant charge, but contribute to its ballistic properties as well. Upon firing, the cases are consumed, leaving no smoldering residue. The use of these combustible cases saves metal, reduces the hazards of spent casings, eliminates the disposal of spent cases and simplifies automatic firing equipment. It is particularly advantageous to avoid spent cases after firing when space is limited such as in the close quarters of a tank.
Various methods and apparatus for forming combustible ordinance items are known in the prior art and described in U.S. Pat. No. 3,320,886. By that method combustible cartridge cases have been made by accreting nitrocellulose fibers and other cellulose fibers from an aqueous suspension onto a porous felting die or preformer, removing excess moisture and then placing the formed felted product in a die-dry press between a male and female die. The felted product was then compressed and die dried between these heated dies at a temperature not exceeding 250.degree. F. The resultant die dried article was then impregnated with a solvent solution of a resin, and cured.
The prior art process of making the combustible cartridge required molding two separate parts which were then assembled to form the cartridge. Such additional handling of the article can increase cost and increase the danger of explosion as the article must be handled a plurality of times.
The forming and assembly of two separate parts is a serious problem with the prior art technique. One end of a finished shell casing is usually completely or partially closed and the other end is shaped to a reduced diameter to facilitate the attachment of a metal stub base. Such a reduced diameter shape amounts to an undercut or a backdraft of the casing. Such a shape cannot be formed by pulp molding techniques because the formed product can not be removed from the male die. To avoid this impasse, the prior art forms at least two molded fiber parts, a top or cap and a bottom, which are later joined by gluing, strapping or the like. Creating the joint requires careful lathe cutting of this highly flammable product. This is a dangerous procedure.
Accordingly, a need exists in the art for a simple and economical method and apparatus for manufacturing a combustible cartridge case or the like with a single molding. Furthermore, a need exists in the art for a single molded fiber product which can readily receive a metal stub base and for a tool which can form such a product.